The present invention relates generally to loudspeakers, and, more particularly, to an improvement in planar-type loudspeakers utilizing a substantially flat diaphragm.
In recent years, certain advances in dynamic loudspeaker design have been provided by the advent of planar diaphragm loudspeakers. Such loudspeakers utilize a relatively stiff and substantially planar (or flat) diaphragm supported by a frame. A voice coil assembly or electromagnetic driver is coupled to the rear surface of the diaphragm. The voice coil or driver acts like a piston, pressing on a circular plate called a hammer, which, in turn, vibrates the diaphragm to produce sound. Typically, the planar diaphragm is constructed of a pre-expanded cellular plastic material, such as polystyrene or styrofoam. The frequency response of a planar diaphragm generally is determined by the type and density of its material, and the area, thickness and contour of its sound producing region. An example of such a planar diaphragm loudspeaker is shown and described in U.S. patent application Ser. No. 08/153,925, filed Nov. 18, 1993 in the name of Alejandro Bertagni et al., which is incorporated herein by reference. Other examples of planar diaphragm loudspeakers are shown and described in U.S. Pat. Nos. 4,003,449 and 4,997,058, both issued in the name of Jose J. Bertagni.
When electric signals are passed through the voice coil assembly, it vibrates the hammer and the diaphragm to produce sound. While the voice coil provides the vibrations necessary to generate sound, it also generates heat as a byproduct. Because the voice coil is coupled to the planar diaphragm, the heat from the voice coil can be conducted to and damage the planar diaphragm. In particular, it has been found that if the amount of heat conducted to the planar diaphragm causes its temperature to rise above approximately 85 degrees celsius, the diaphragm will cavitate or melt and the speaker will fail.
One attempt to avoid heat damage to the diaphragm material was to insert an insulating material, such as a combination of cork and neoprene, in the form of a disk between the hammer and the diaphragm. This insulating disk would act as a heat barrier or insulator to slow down the conduction of heat to the diaphragm. However, if the output power of the voice coil assembly was maintained or increased, the heat would rise sufficiently to cause failure of the diaphragm.
Accordingly, there exists a need for a planar diaphragm loudspeaker that conveys a reduced amount of heat through the coupling between its voice coil assembly and its planar diaphragm. The present invention fulfills this need.